A structure in which a semiconductor wafer is electrostatically chucked, and helium gas is caused to flow between the semiconductor wafer and en electrode has been widely used as a technique for accurately securing temperature of the semiconductor wafer in a plasma processing apparatus such as a plasma etching apparatus.
Two systems of unipolar (monopole) and bipolar (dipole) systems, for example, are mainly used as an electrostatic chuck system. A unipolar system applies an electrostatic chucking voltage to one electrode, and a bipolar system is provided with two or more electrodes and applies electrostatic chucking voltages having different polarities.
The electrostatic chuck is implemented by applying a DC voltage between an electrode and a semiconductor wafer with a thin insulating film, formed using ceramic or the like, interposed therebetween. In addition, a high voltage is applied to the semiconductor wafer in order to allow ions from plasma to be accelerated and incident.
Japanese Patent Application Laid-Open Publication No. 2006-210726 (Patent Document 1) discloses a method of monitoring a radio-frequency voltage which is being applied to an electrode, and controlling an output voltage of a power supply for electrostatic chuck (ESC) based on a monitored radio-frequency voltage signal, thereby keeping a voltage to be applied at the electrostatic chuck in a desired value.
In addition, Japanese Patent Application Laid-Open Publication No. 2013-12624 (Patent Document 2) discloses a technique of alternately applying two types of voltages, that is, applying a high voltage and a low voltage of a radio-frequency voltage to a semiconductor wafer, and performing etching by setting a time ratio (TM duty) of high power and a repetition frequency. At this time, Patent Document 2 discloses that a value at the time of high power is a stable value as a peak value of the radio-frequency bias voltage to be applied to the wafer to be monitored.
Further, Japanese Patent Application Laid-Open Publication No. 2010-10236 (Patent Document 3) discloses a technique regarding control of an output voltage of a power supply for electrostatic chuck in a case in which a radio-frequency bias voltage, which is not time modulated, is applied to an electrode in a plasma processing apparatus.